South Korea’s Slumping Corals Alarm Divers as Scientists Study Climate Effects

Ko Myeong-hyo remembers the soft corals off Jeju Island as a vivid underwater garden, full of color and marine life. She began diving there six years ago to harvest seafood for sale. After two years of rising temperatures and harsher weather, many of the corals have sagged, collapsed and died.

“Watching the coral garden collapse and turn white, it was so disorienting,” Ko said. “I was afraid the whole sea might be collapsing.”

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Watching the coral garden collapse and turn white, it was so disorienting.

The slumping has appeared again this year, according to the Paran Ocean Citizen Science Center, a group of divers that monitors the soft corals around Jeju’s UNESCO-listed sites, mostly near uninhabited islets south of the island. The group said roughly half of one colony near Beomseom has struggled in recent months.

Soft corals differ from hard corals because they lack rigid calcium carbonate skeletons. They depend on internal fluid pressure to remain upright. Environmental changes can disrupt that pressure, causing the corals to sag or collapse. Researcher Kim Taihun warned that repeated large-scale slumping could leave the colonies less able to recover as sections break away and deteriorate.

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I was afraid the whole sea might be collapsing.

Kim and Korea Institute of Ocean Science and Technology researcher Anna Beate Jöst documented Jeju’s 2024 slumping event in a May article published in Scientific Reports. The Korea Heritage Service said it had monitored the situation this year and would continue long-term research. The Oceans Ministry said it planned a detailed investigation to assess the damage.

Kim said this year’s event resembled the 2024 episode but could worsen if high water temperatures continue through September. He also said El Nino could bring typhoons and heavy rain. Researchers are examining weather conditions and freshwater flowing from China’s Yangtze River, which could affect local salinity. Kim called for consistent, quantitative monitoring, citing limited research support. Jeju’s soft coral communities live near the northern edge of coral distribution in the East China Sea and serve as a nursery for the island’s marine ecosystem.

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If another large-scale slumping happens, corals partially recover and then a lot break off and deteriorate again, and that keeps repeating, their capacity to recover just keeps declining.